AbstractID: 7268 Title: Determination of organ motion and patient setup error
using an in-line CT in external beam radiation treatment
We are investigating the use of an in-line CT for determination and correction of
organ motion and patient setup error. The CT shares a common treatment
couch with the linear accelerator which allows the patient to be aligned under the
treatment lasers and then imaged following a series of fixed treatment couch
motions. The verification CT data set can then be compared to the original
treatment planning CT data set to detect and quantify deviations. The analysis is
automated using mutual information based registration. A sequential series of
scans of an anthropomorphic phantom was used to determine the reproducibility
of the system. The couch motion can be reproduced to one pixel dimension (0.89
mm). A geometric phantom on a precision mount was used to acquire scans of
precise orthogonal shifts to test the ability of the system to determine known
offsets. The average difference between the known and measured orthogonal
shifts was less than 1 mm. A sequential series of verification CT data sets were
acquired for patients receiving external beam prostate therapy to determine
organ motion and setup error. The imaging adds 10 minutes to the patient
treatment time. Organ motion and setup error were determined from the
verification data by first registering to the bony anatomy and then to only the
prostate tissue. Preliminary results will be reported.